This is the situation at the beginning of the 20th century. There where only two categories, officers and enlisted. The enlisted had only four ranks; private, pfc, corporal and sergeant. Brigadier Generals had one silver star, while Major Generals had one gold star.

In 1912 the enlisted category was divided into primary enlisted and secondary enlisted. The first category contained privates, pfc and corporals; the second category sergeants and the new ranks of brigada and suboficial.

In 1934 the ranks of Subayudante and Sargento Primero was abolished, and Sargento became a NCO rank. The rank of Subteniente was abolished in 1935. 1939 the two top general ranks where restored. 1940 Cabo Primero was added to the enlisted ranks. The crowns above the generals' rank stars where returned in 1942. The following year, the white star of General de Brigada was changed into a yellow, and the number of stars was increased with one for each rank above.

Source: as above, where images of the situation after each of these changes can be found.

The ranks of Primo Sargento and Subteniente where reintroduced in 1960. With the death of Franco and the factual re-establishment of monarchy, the Bourbon crowns where restored to the generals' rank insignia in 1976. In 1986 the placement of the rank insignia was moved from the cuffs, to the epaulets.

The beginning transformation of the Spanish army from a conscript army to a volunteer army is shown by the introduction of special rank insignia that separates national servicemen from professional soldiers in the most junior ranks. Soldado profesional is given the old rank insignia of Pfc, and replacement corporal is placed between this rank and corporal.

1999 would see yet another rank adjustment. By that year the Captain General rank became a 5-star rank, as always held by the King of Spain in his constitutional duty as Commander in Chief of the Armed Forces, and the 4 star rank became that of a General of the Army.

The rank of Corporal Major, created that same year, became the highest enlisted rank, and the rank of Private First Class was reinstated.

These are from the General Branch, and now towards the Navy Corps of Engineers, Specialists Branch and the Logistics Branch, all staff corps manned by officers with ratings provided by the General Branch.